Global, regional, and national estimates of levels of preterm birth in 2014: a systematic review and modelling analysis oleh Saifon Chawanpaiboon, MD, Joshua P Vogel, PhD, Ann-Beth Moller, MPH, Pisake Lumbiganon, ProfMD, Max Petzold, ProfPhD, Daniel Hogan, PhD, Sihem Landoulsi, MSc, Nampet Jampathong, MPH, Kiattisak Kongwattanakul, MD, Malinee Laopaiboon, ProfPhD, Cameron Lewis, MBBS, Siwanon Rattanakanokchai, MPH, Ditza N Teng, MBBS, Jadsada Thinkhamrop, ProfMD, Kanokwaroon Watananirun, MD, Jun Zhang, ProfPhD, Wei Zhou, MD, A Metin Gülmezoglu, PhD